1. Field of the Invention
The present invention relates generally to an apparatus and a method for a power transmitter in a wireless communication system. More particularly, the present invention relates to an apparatus and a method for an Envelope Elimination and Restoration (EER) power transmitter in a wireless communication system.
2. Description of the Related Art
As wireless communication systems are advancing in accordance with advances in communication technologies, the amount of data transmitted by a wireless communication system and the transmission rate of the data are increasing. Furthermore, with the increased data and transmission rate, a bandwidth of a signal to transmit is widened and a Peak to Average Power Ratio (PAPR) increases. Accordingly, the importance of a high-performance transmitter having high efficiency and high linearity is growing in the wireless communication system.
However, since the efficiency and the linearity of a conventional power transmitter are inversely related, it is difficult to meet both the efficiency and the linearity demands of the communication system using the conventional power transmitter.
To address this problem, research is being conducted on an Envelope Elimination and Restoration (EER) power transmitter. The EER power transmitter modulates a phase component, from which an amplitude component is removed from the signal to be amplified to a Radio Frequency (RF) signal, and amplifies the modulated signal as shown in FIG. 1. This method achieves high-efficiency amplification with a reduction in distortion of the amplifier.
FIG. 1 depicts a conventional EER power transmitter.
The EER power transmitter of FIG. 1 includes a signal separator 100, a bias modulator 110, an orthogonal modulator 120, and a high-efficiency power amplifier 130.
The signal separator 100 separates an amplitude component and a phase component of the signal to be amplified. The signal separator 100 outputs the amplitude component to the bias modulator 110 and outputs the phase component to the orthogonal modulator 120.
The bias modulator 110 amplifies the amplitude component fed from the signal separator 100 and outputs the amplified amplitude component to the high-efficiency power amplifier 130. The bias modulator 110 includes a linear amplitude amplifier (not shown) and a switching regulator (not shown).
The orthogonal modulator 120 modulates the phase component fed from the signal separator 110 into an RF signal.
The high-efficiency power amplifier 130 amplifies the RF signal output from the orthogonal modulator 120 using the signal output from the bias modulator 110 as the drain bias. By merely amplifying the phase component output from the orthogonal modulator 120, the high-efficiency power amplifier 130 can reduce the distortion of the amplifier. In addition, using the amplified amplitude component provided from the bias modulator 110 as the drain bias, the high-efficiency power amplifier 130 can restore the amplitude component of the signal to be amplified.
As stated above, the EER power amplifier amplifies only the phase component using the amplitude component of the transmit signal as the bias voltage, to thus attain high efficiency and high linearity of the power transmitter.
To address both the efficiency and linearity in an EER power amplifier, the bias modulator should be able to accommodate the wide bandwidth and the high PAPR of the amplitude component. In other words, the bias modulator needs to accommodate a rapid change of a slew rate with high efficiency.
However, the switching regulator, which is the main power source of the bias modulator, cannot supply the current corresponding to the wide change of the slew rate. Accordingly, since the bias modulator provides the current to the high-efficiency power amplifier by increasing the current transfer rate of the linear amplitude amplifier that has lower efficiency than the switching regulator, there is a limitation in improving the total efficiency of the EER power transmitter.
Accordingly, there is a need for an improved apparatus and a method that enhances efficiency of a bias modulator in an EER power transmitter.